<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <button>点我</button>

</body>
<script>
  const btn = document.querySelector("button")
  // btn.onclick = function () {
  //   console.log('123  ----->  ', 123);
  // }

  // btn.onclick = () => {
  //   alert(123)
  //   return 
  // }

  btn.onclick = () => {
    // 💥 下方语句从右向左执行, 等同于上方代码
    return alert(123)
  }

  // 💥 return 和 {}, 可以同时省略掉
  btn.onclick = () => alert(123)

</script>

</html>